Magnetoresistance element and non-volatile semiconductor storage device using same magnetoresistance element

ABSTRACT

The invention provides a magnetoresistance element with a configuration such that a stable switching action is possible with a current flowing in response to the application of a unipolar electrical pulse, and a non-volatile semiconductor storage device using the magnetoresistance element. 
     A magnetoresistance element  1 - 1  includes a magnetic tunnel junction portion  13  configured by sequentially stacking a perpendicularly magnetized first magnetic body  22 , an insulation layer  21 , and a perpendicularly magnetized second magnetic body  200 . The second magnetic body  200  has a configuration wherein a ferromagnetic layer and a rare earth-transition metal alloy layer are stacked sequentially from the insulation layer  21  side interface. A heat assist layer  28 - 1  that heats the second magnetic body  200  with a heat generated based on a current flowing through the magnetic tunnel junction portion  13  is further provided, and the magnetization direction of the second magnetic body  200  is reversed by the heating of the second magnetic body  200 . A non-volatile semiconductor storage device  10 - 1  includes the magnetoresistance element  1 - 1 , a switching element connected in series to the magnetoresistance element  1 - 1 , information rewriting means that carries out a write and erase by causing a write current to flow through the magnetoresistance element  1 - 1 , and reading means that reads information stored from the amount of current flowing through the magnetoresistance element  1 - 1.

TECHNICAL FIELD

The present invention relates to a magnetoresistance element forming acentral portion of a magnetic memory (MRAM), and to a non-volatilesemiconductor storage device using the magnetoresistance element.

BACKGROUND ART

In recent years, there has been a noticeable increase in capacity ofnon-volatile semiconductor storage devices typified by flash memories,going as far as the release of products having a capacity of severalhundred gigabytes being announced. The product value of the non-volatilesemiconductor storage device is increasing, in particular as storage forUSB memories and mobile telephones. Also, the non-volatile semiconductorstorage device utilizes the fundamental advantages peculiar to a solidstate memory—vibration resistance, high reliability, and low powerconsumption—and is becoming mainstream as a storage device for mobiletype or portable type electronic instruments for music and images.

Meanwhile, apart from the heretofore described storage-orientedapplication, research is being vigorously carried out aimed at, bygiving non-volatility to a DRAM currently being used as a main memory ofan information instrument, realizing a computer, a so-called “instant-oncomputer”, that starts up instantly when used and whose powerconsumption is unrestrictedly zero when waiting. In order to realizethis, a memory that satisfies requirements of (1) a switching speed lessthan 50 ns and (2) a rewrite quantity exceeding 10¹⁶, which aretechnical specifications required as a DRAM, and that includesnon-volatility, is said to be necessary.

As candidates for this kind of next generation non-volatilesemiconductor storage device, research and development is being carriedout on non-volatile memory elements based on various kinds of principle,such as a ferroelectric memory (FeRAM), a magnetic memory (MRAM), and aphase-change memory (PRAM). Even among these kinds of non-volatilememory, the MRAM is seen as being promising as a candidate thatsatisfies the heretofore described technical specifications forreplacing the DRAM. The rewrite quantity (>10¹⁶) cited in the heretoforedescribed technical specifications is a figure assumed based on anaccess quantity when continuing to access at 30 ns for 10 years.However, as no refresh cycle is necessary when the memory isnon-volatile, it may be that such a large quantity is not necessary. TheMRAM is at the prototype level but, as it has achieved a rewritequantity of 10¹² or more and the switching speed thereof is high (<10ns), feasibility is seen as being particularly high in comparison withtechnologies forming other candidates as a non-volatile semiconductorstorage device.

Problems with the MRAM are that the cell area is large and that thewrite energy is large. As the currently commercialized small capacity(in the region of 4 Mbit) MRAM is a current produced magnetic fieldrewrite type, the cell area thereof is far too large at 20 to 30F² (F isthe minimum processing dimension in the manufacturing process) or more,because of which, it is not practical as DRAM replacement means. Inresponse to this, two breakthrough technologies are in the process ofchanging the situation. One is an MTJ (magnetic tunnel junction) usingan MgO tunnel insulation film, and according to the MTJ, amagnetoresistance of 200% or more is easily obtained (for example, referto Non-patent Document 1). The other is a spin torque transfer method(hereafter abbreviated to STT method). According to the STT method, asit is possible to avoid an increase of reversed magnetic fields inminute cells, which is fatal with the current produced magnetic fieldrewrite method, it is possible to reduce write energy due to scaling.According to the STT method, as one transistor to one MTJ is ideallypossible, it is assumed that the cell area is equivalent to that of theDRAM (6 to 8F²) (for example, refer to Patent Document 1, Non-patentDocument 2).

Herein, a simple description will be given, using FIG. 11, of an actionof the heretofore described heretofore known MRAM. FIG. 11 is anenlarged sectional view of a storage device 10 showing a portionincluding a magnetoresistance element 1. The storage device 10 shown inFIG. 11 carries out an action equivalent to that described in PatentDocument 1.

The magnetoresistance element 1 has a magnetic tunnel junction (MTJ)portion 13, and is configured in such a way that the MTJ portion 13 issandwiched by a lower electrode 14 and an upper electrode 12. The MTJportion 13 is of a structure wherein a pinned layer 22 (a first magneticbody), an insulation layer 21, a storage layer 20 (a second magneticbody), and the upper electrode 12 are stacked sequentially from below(the lower electrode 14 side). The pinned layer 22 and storage layer 20are formed of perpendicularly magnetized films. The lower electrode 14is disposed on a drain region 24 formed in a silicon substrate 15, andfurthermore, a source region 25 is formed in the silicon substrate 15 ata distance from the drain region 24. Agate line 16 is formed in aportion above the drain region 24 and source region 25, isolated fromthem, and a MOS-FET is configured of the drain region 24, source region25, and gate line 16. Furthermore, a contact portion 17 and a wordportion 18 are stacked sequentially on the source region 25, and theword line 18 is connected to an unshown control circuit. Also, the upperelectrode 12 is connected to a bit line 11, and the bit line 11 is alsoconnected to the unshown control circuit. The bit line 11 and word line18 are isolated from each other by an interlayer insulation film 23.

Next, a description will be given, using FIG. 12, of an operatingprinciple of the heretofore known magnetoresistance element 1. FIG. 12is an enlarged view of the MTJ portion 13 in FIG. 11.

In the magnetoresistance element 1 configured as in FIG. 12, theresistance value changes in accordance with a relative magnetizationdirection of the storage layer 20 with respect to the pinned layer 22 (aTMR effect). Specifically, when the magnetization direction of thestorage layer 20 is a direction opposite to that of the pinned layer 22(the condition of FIG. 12(a)), the insulation layer 21 is in a highresistance condition, while when the magnetization direction of thestorage layer 20 is the same direction as that of the pinned layer 22(the condition of FIG. 12(b)), the insulation layer 21 is in a lowresistance condition. Utilizing this, a high resistance condition iscaused to correspond to “0” and a low resistance condition to “1”, andthe magnetization condition (data) of the storage layer 20 is read as aresistance value. This is the read principle.

With regard to a write, by causing a current 103 oriented from thestorage layer 20 toward the pinned layer 22 to flow, as in FIG. 12, thestorage layer 20 changes from a high resistance condition to a lowresistance condition. Also, by causing an oppositely oriented current toflow through the storage layer 20 when it is in a low resistancecondition, the layer 20 changes from a low resistance condition to ahigh resistance condition. This is the write principle (refer toNon-patent Document 2). In the way heretofore described, the storagedevice 10 selects the magnetoresistance element 1 using a correspondingMOS-FET, reads information stored in the magnetoresistance element 1,and writes information into the magnetoresistance element 1.

Meanwhile, there is also a proposal for one diode to one MTJ, aiming ata small cell area (up to 4F²) equivalent to that of a flash memory (forexample, refer to Patent Document 2). Furthermore, there is also aproposal whereby, in an element provided with a drive layer whosemagnetization direction is essentially fixed in the stacking direction,transistors are reduced from two kinds to one kind, thus achieving asimplification of the circuit, by arranging in such a way that thepolarity of the current is in one direction only, and owing to thecircuit configuration of one transistor to one MTJ obtained thereby, acell size equivalent to the cell size of a DRAM is realized (forexample, refer to Patent Document 3).

RELATED ART DOCUMENTS Patent Documents

-   Patent Document 1: JP-A-2008-28362-   Patent Document 2: JP-A-2004-179483-   Patent Document 3: JP-A-2006-128579

Non-Patent Documents

-   Non-patent Document 1: D. D. Djayaprawira et al, “230%    room-temperature magnetoresistance in CoFeB/MgO/CoFeB magnetic    tunnel junctions”, Applied Physics Letters, Vol. 86, 092502, 2005-   Non-patent Document 2: J. Hayakawa et al, “Current-induced    magnetization switching in MgO barrier based magnetic tunnel    junctions with CoFeB/Ru/CoFeB synthetic ferromagnetic free layer”,    Japanese Journal of Applied Physics, vol. 45, L1057-L1060, 2006-   Non-patent Document 3: D. H. Lee et al, “Increase of temperature due    to Joule heating during current-induced magnetization switching of    an MgO-based magnetic tunnel junction”, Applied Physics Letters,    Vol. 92, 233502, 2008

SUMMARY OF THE INVENTION Problems that the Invention is to Solve

However, as the heretofore described proposal of one diode to one MTJmeans carrying out a switching with a current under a forward bias and areverse bias via a diode, or more specifically, as it means carrying outa switching with a current under a forward bias (a forward current) anda leakage current under a reverse bias, the principle remains onewherein switching is carried out in accordance with electrode polarity.Essentially, the diode is formed in order to carry out an MTJ selectionin a write, erase, and read action without disturbance. Because of this,leakage current flows not only in a reverse direction but also in aforward direction. Consequently, with the heretofore described proposalthat has switching with a leakage current under a reverse bias as anoperating principle, current with a value in the region of that used inthe switching also flows at a time of low voltage when there is aforward bias, and the disturbance preventing effect is insufficient.That is, as the current also flows at a time of low voltage when thereis a forward bias when carrying out a switching with a leakage currentunder a reverse bias, there occurs the same kind of disturbance problemas with a simple matrix type memory with no element selector switch, andit is impossible to realize a highly integrated element. In this way, inorder to realize a cross-point type memory using one diode to one MTJhaving the minimum cell area 4F², it is not possible to employ theheretofore known STT method that has switching in accordance withcurrent polarity as an operating principle.

Also, the proposal described in Patent Document 2 of one transistor toone MTJ circuit using an element provided with a drive layer whosemagnetization direction is essentially fixed in the stacking directionis a method whereby switching is carried out by inducing a spinprecession with a spin injection from the drive layer to a free layer.However, with the principle whereby a spin precession is induced with aspin injection from the drive layer, there is a problem in that theorientations (parallel or anti-parallel) of the free layer (storagelayer) and pinned layer (magnetization fixed layer) are liable to bebiased toward one. Furthermore, as there is also concern about themagnetization orientation of the pinned layer (magnetization fixedlayer) changing, a problem occurs in that, even when realizing a rewritequantity equivalent to that of a DRAM, reliability decreases. Because ofthis, it is difficult to realize a one transistor to one MTJ circuitwherein switching is carried out under a condition that the current hasonly one polarity.

The invention, having been contrived bearing in mind the heretoforedescribed problems, has an object of providing a magnetoresistanceelement with a configuration such that a stable switching action ispossible with a current flowing in response to the application of aunipolar electrical pulse, and a non-volatile semiconductor storagedevice using the magnetoresistance element.

Means for Solving the Problems

The inventors of the present application, as a result of examining theheretofore described problems by returning to the operating principle ofa spin torque transfer (STT) method in a magnetoresistance element, havearrived at the invention of a magnetoresistance element, and anon-volatile semiconductor storage device using the magnetoresistanceelement, shown hereafter.

That is, a first magnetoresistance element according to the inventionincludes a magnetic tunnel junction portion configured by sequentiallystacking a perpendicularly magnetized first magnetic body, an insulationlayer, and a perpendicularly magnetized second magnetic body, and ischaracterized in that the second magnetic body has a configurationwherein a ferromagnetic layer and a rare earth-transition metal alloylayer are stacked sequentially from the insulation layer side interface,a heat assist layer that heats the second magnetic body with a heatgenerated based on a current flowing through the magnetic tunneljunction portion is further provided, and the magnetization direction ofthe second magnetic body is reversed by the heating of the secondmagnetic body.

In the heretofore described configuration, the second magnetic body thatrecords data as a magnetization direction is heated by the heat assistlayer when writing, changing the magnetization direction thereof. Bycontrolling the magnetization direction of the second magnetic body viathe temperature of the second magnetic body heated by the heat assistlayer, a switching action with a unipolar electrical pulse is possible.

A second magnetoresistance element according to the invention includes amagnetic tunnel junction portion configured by sequentially stacking aperpendicularly magnetized first magnetic body, an insulation layer, anda perpendicularly magnetized second magnetic body, and is characterizedin that the first magnetic body has a configuration wherein aferromagnetic layer and a rare earth-transition metal alloy layer arestacked sequentially from the insulation layer side interface, a heatassist layer that heats the first magnetic body with a heat generatedbased on a current flowing through the magnetic tunnel junction portionis further provided, and the magnetization direction of the firstmagnetic body is reversed by the heating of the first magnetic body.

In the heretofore described configuration, the first magnetic body isheated by the heat assist layer when writing, changing the magnetizationdirection thereof around a compensated temperature. By controlling themagnetization direction of the first magnetic body via the temperatureof the first magnetic body heated by the heat assist layer, a switchingaction with a unipolar electrical pulse is possible.

A non-volatile semiconductor storage device according to the inventionis characterized by including the heretofore described magnetoresistanceelement, a switching element connected in series to themagnetoresistance element, information rewriting means that carries outa write and erase by causing a write current to flow through themagnetoresistance element, and reading means that reads informationstored from the amount of current flowing through the magnetoresistanceelement.

According to the heretofore described non-volatile semiconductor storagedevice, as it is possible to carry out a switching with a unipolarelectrical pulse, it is possible to configure a 4F² sized memory cellformed from one diode and one MTJ. Because of this, it is possible toprovide a highly integrated, high performance non-volatile semiconductorstorage device at a low cost.

Advantage of the Invention

According to the invention, it is possible to provide amagnetoresistance element with which it is possible to carry out astable switching action with a write current based on a unipolarelectrical pulse. Also, according to the invention, it is possible toprovide a small, highly reliable non-volatile semiconductor storagedevice using the heretofore described magnetoresistance element.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing a configuration of amagnetoresistance element according to a first embodiment of theinvention.

FIG. 2 is a graph showing magnetization-temperature characteristics ofthe magnetoresistance element according to the first embodiment.

FIGS. 3A, 3B, 3C, and 3D illustrate schematic diagrams showing anoperating principle of the magnetoresistance element according to thefirst embodiment.

FIGS. 4A, 4B, 4C, and 4D illustrate schematic diagrams showing anoperating principle of a magnetoresistance element according to a secondembodiment.

FIG. 5a is a sectional view showing a first fabrication step of themagnetoresistance element according to the first embodiment.

FIG. 5b is a sectional view showing a second fabrication step of themagnetoresistance element according to the first embodiment.

FIG. 5c is a sectional view showing a third fabrication step of themagnetoresistance element according to the first embodiment.

FIG. 5d is a sectional view showing a fourth fabrication step of themagnetoresistance element according to the first embodiment.

FIG. 5e is a sectional view showing a fifth fabrication step of themagnetoresistance element according to the first embodiment.

FIG. 5f is a sectional view showing a sixth fabrication step of themagnetoresistance element according to the first embodiment.

FIG. 5g is a sectional view showing a seventh fabrication step of themagnetoresistance element according to the first embodiment.

FIG. 6 is a sectional view showing a configuration of themagnetoresistance element according to the second embodiment of theinvention.

FIG. 7 is a graph showing change in resistivity of a metal-insulatortransition material;

FIG. 8 is a graph illustrating an action of a magnetoresistance elementaccording to a third embodiment.

FIG. 9 is a schematic diagram showing a memory cell using themagnetoresistance elements shown in FIG. 1 and FIG. 6.

FIG. 10 is a schematic diagram showing a non-volatile semiconductorstorage device including a cross-point type memory cell array formed byarraying memory cells.

FIG. 11 is a sectional view showing an example of a configuration of amagnetoresistance element according to a heretofore known technology.

FIGS. 12A and 12B illustrate schematic diagrams showing an operatingprinciple of the magnetoresistance element according to the heretoforeknown technology.

MODE FOR CARRYING OUT THE INVENTION

Hereafter, a description will be given, based on the drawings, ofembodiments of a magnetoresistance element according to the invention,and a storage device using the magnetoresistance element.

First Embodiment

FIG. 1 is a partial enlarged sectional view of a storage device 10-1showing a portion in which is disposed a magnetoresistance element 1-1according to the invention. In FIG. 1, components the same as componentsshown in FIG. 11 are given the same reference numerals, and adescription thereof is omitted. The configuration of themagnetoresistance element 1-1 in the first embodiment differs from thatof a heretofore known magnetoresistance element 1 in that a storagelayer 200 (a second magnetic body) is used instead of a storage layer 20of the magnetoresistance element 1 shown in FIG. 11, and that a heatassist layer 28-1 is deposited on the storage layer 200. In theembodiment, the storage layer 200 and a pinned layer 22 are each formedof a perpendicularly magnetized film.

The storage layer 200 is configured of a ferromagnetic layer (not shown)and a rare earth-transition metal alloy layer (not shown) stackedsequentially from an insulation layer 21 side interface. Theferromagnetic layer is formed of an N-type ferrimagnetic body.

Meanwhile, the heat assist layer 28-1 is formed of a normal resistivematerial, as will be described hereafter. The heat assist layer 28-1 isdisposed in a way such as to make contact with an interface on the sideof the storage layer 200 opposite to the insulation layer 21 sideinterface.

As an operating principle of a read of the magnetoresistance element 1-1is the same as that of the heretofore known magnetoresistance element, adescription thereof will be omitted.

Next, a description will be given of a principle whereby a write actionusing a unipolar electrical pulse is possible with the magnetoresistanceelement 1-1 configured in such a way. In the embodiment, as has alreadybeen described, an N-type ferrimagnetic body is used as theferromagnetic layer in the storage layer 200. The N-type ferrimagneticbody has the kind of magnetization-temperature characteristics shown inFIG. 2. An important point is that when a certain temperature (acompensated temperature T_(comp)) is exceeded, the magnetizationdirection of the storage layer 200 is reversed. Herein, it is taken thatthe compensated temperature of the storage layer 200 is approximately110° C. The compensated temperature can easily be set by adjusting thecomposition ratios of the rare earth element and transition metalelement in the rare earth-transition metal alloy layer in the storagelayer 200. This is also one reason for using a rare earth-transitionmetal alloy in the storage layer 200.

For a write action from a high resistance condition to a low resistancecondition, a spin torque transfer (STT) action the same as in theheretofore known magnetoresistance element is carried out. That is, asshown in FIG. 11, in the heretofore known magnetoresistance element, thestorage layer 20 changes from a high resistance condition (FIG. 11 (a))to a low resistance condition (FIG. 11 (b)) by a current 103 beingcaused to flow from the storage layer 20 (a second magnetic body) towarda pinned layer 22 (a first magnetic body). In the storage layer 200 inthe embodiment too, it is possible to cause a change from a highresistance condition to a low resistance condition by causing the samekind of current to flow.

Hereafter, a description will be given, using FIG. 3, of a write actionfrom a low resistance condition to a high resistance condition. In FIG.3, arrows 102 and 102A indicate magnetization directions. The heatassist layer 28-1 shown in FIG. 1 is omitted from FIG. 3.

Firstly, when a write current flows, Joule heat is generated owing tothe resistance (up to 4 kΩ) of the heat assist layer 28-1, the heat istransmitted from the heat assist layer 28-1 to the storage layer 200,and the storage layer 200 is heated (FIG. 3(a)). When the temperature ofthe storage layer 200 exceeds the compensated temperature T_(comp) owingto the heating, the net magnetization of the storage layer 200 isreversed (FIG. 3(b)). By an STT action being carried out in thiscondition, the storage layer 200 receives a torque directed in the samedirection as the pinned layer, and reverses the magnetization directionat this point (FIG. 3(c)). When the supply of the write current stops,the temperature of the storage layer 200 decreases, and the reversedmagnetization returns to the original condition when the temperaturebecomes lower than the compensated temperature T_(comp). Because ofthis, the magnetization directions of the storage layer 200 and pinnedlayer 22 are opposed directions, and the write action from the lowresistance condition to the high resistance condition is completed (FIG.3(d)).

Herein, for example, TbCo, GdCo, GdFeCo, TbFeCo, or the like, ispreferably used as the material of the rare earth-transition metal alloylayer in the storage layer 200 (the second magnetic body) and, forexample, a spin-polarized material such as Fe, FeCo, FeCoB, or the like,is preferably used as the material of the ferromagnetic layer in thestorage layer 200. As the rare earth-transition metal alloy layer issuch that, as previously described, the compensated temperature caneasily be adjusted using the composition thereof, the heretoforedescribed action is easily realized, and also, as the rareearth-transition metal alloy layer has a large amount of perpendicularmagnetic anisotropic energy (10⁵ to 10⁶ erg/cc), it can store data for along period.

It is assumed that the spin-polarized material used as the material ofthe ferromagnetic layer indicates one of the following two kinds ofalloy.

(1) A material with a high spin-polarization rate (for example, a halfmetal such as a Heusler alloy)

(2) A magnetic body wherein the spin is completely polarized withrespect to a Δ1 band, as with, for example, Fe, FeCo, FeCoB, or thelike.

The reason for including the magnetic body of (2), whosespin-polarization rate is not so high, in the spin-polarized materialsis as follows. That is, it is because, when a spin tunnel junction isconfigured by combining the magnetic body (Fe, FeCo, FeCoB, or the like)of (2) with an insulation layer (for example, an insulation layer formedfrom Mg) having four-fold symmetry with respect to the stackingdirection, the insulation layer acts in such a way as to selectivelyallow the Δ1 band conduction electrons to pass through, and it ispossible to increase the effective spin-polarization rate. With thiskind of configuration using FeCo, or the like, it is both theoreticallyand experimentally demonstrated that, by optimizing the conditions; amagnetoresistance ratio in the region of 1000% is obtained.

Meanwhile, it is desirable that the heat assist layer 28-1 is given aresistance value in the region of 1 kΩ to 50 kΩ. As an STT type writecurrent in an MRAM is in the region of 0.5 to 1×10⁶ A/cm², the elementtemperature exceeds 500° C. when the resistance value of the heat assistlayer 28-1 exceeds 50 kΩ, and there is a danger of element breakup.Also, when the resistance value of the heat assist layer 28-1 is in theregion of a few hundred Ohms, the temperature rise decreases (a fewdegrees Celsius), and the heretofore described action becomes difficult.Therefore, a range of 1 kΩ to 50 kΩ is good for the resistance value ofthe heat assist layer 28-1. Then, when considering the fabricationprocess, it is desirable that the heat assist layer 28-1 is rather thin(10 to 20 nm). Based on the above, a material having a resistivity of0.01 Ωcm to 10 Ωcm is appropriate as the heat assist layer 28-1. Forexample, TaN_(x), TaO_(x), TiO_(x), or the like, are included as thiskind of material.

Next, a description will be given, referring to FIG. 5a to FIG. 5g , ofa fabrication method of the magnetoresistance element according to thefirst embodiment.

Firstly, a drain region 24, a source region 25, a gate line 16, acontact portion 17, a word line 18, a lower electrode 14, and aninsulation body 23A are formed on a silicon substrate 15 using a normalCMOS process (FIG. 5a ).

Next, as shown in FIG. 5b , after stacking the pinned layer 22(Tb₁₆Fe₅₉Co₂₅ of 5 nm thickness, Fe₁₀Co₉₀ of 1 nm thickness), theinsulation layer 21 (MgO of 0.7 nm thickness), and the storage layer 200(Fe₁₀Co₉₀ of 1 nm thickness, Gd₂₂Co₇₈ of 2 nm thickness) using amagnetron sputtering method, the heat assist layer 28-1 (TaN of 20 nmthickness) is deposited using a reactive sputtering method, and finally,an upper electrode 12 (Ta of 2 nm thickness/Ru of 5 nm thickness) isdeposited using a magnetron sputtering method.

Next, a resist 51 is exposed and developed in a circular form with adiameter in the region of 100 nm using photolithography. Next, as shownin FIG. 5c , the sputtered film other than in the resist portion isscraped off using an ion etching. After the resist is removed using asolvent, ashing, or the like, an interlayer insulation film 23B (SiO₂ of60 nm thickness) is deposited (FIG. 5d ). Subsequently, a contact hole52 is formed using photolithography in a portion above the upperelectrode 12 (FIG. 5e , FIG. 5f ). Subsequently, a bit line 11 is formed(FIG. 5g ). In the way heretofore described, it is possible to fabricatea magnetic memory in the first embodiment of the invention. An oxideprotective layer (for example, a Ta layer, a Ru layer, or the like) of afew nanometers may be deposited between the storage layer 200 and heatassist layer 28-1 with an object of suppressing oxygen diffusion fromthe heat assist layer 28-1, allowing a stable action for a longer time.

Next, a description will be given of a specific action of themagnetoresistance element 1-1 according to the embodiment.

The compensated temperature T_(comp) of the Gd₂₂Co₇₈ used in the storagelayer 200 is around 110° C. Therefore, when taking the element size(diameter) to be 100 nm, the heat assist layer 28-1 resistance value tobe 4 kΩ, the current density to be 8×10⁵ A/cm², and the write currentpulse width to be 10 ns, and furthermore, approximating thatapproximately one half of the Joule heat generated in the heat assistlayer 28-1 contributes to the temperature rise of the element, thetemperature of the element 1-1 rises approximately 110° C., andconsequently, when taking room temperature to be 20° C., the actualelement temperature is 130° C. As this is equal to or higher than thecompensated temperature T_(comp), the heretofore described write actionfrom a low resistance condition to a high resistance condition isrealized. Also, when the current density is 6.6×10⁵ A/cm², thetemperature rise is in the region of 75° C., and as the elementtemperature is 95° C., which is lower than the compensated temperatureT_(comp), the write action from a high resistance condition to a lowresistance condition is realized. In this way, depending on the size ofthe write current pulse, it is possible to write both a low resistancecondition and a high resistance condition with a current of the samepolarity.

Second Embodiment

A description will be given, referring to FIG. 6, of a second embodimentof the invention. A magnetoresistance element 1-2 according to thesecond embodiment differs from the first embodiment in that the pinnedlayer 22 (the first magnetic body) in the first embodiment shown in FIG.1 is replaced with a pinned layer 220, a heat assist layer 28-2 isprovided instead of the heat assist layer 28-1 in the first embodiment,and the storage layer 200 (the second magnetic body) in the firstembodiment is replaced with the storage layer 20 shown in FIG. 11.

The pinned layer 220 (a first magnetic body) has the configuration ofthe storage layer 200 of FIG. 1. That is, the pinned layer 220 isconfigured of a ferromagnetic layer and a rare earth-transition metalalloy layer stacked sequentially from the insulation layer 21 sideinterface.

Meanwhile, the heat assist layer 28-2 is formed of the same material asthe heat assist layer 28-1 of FIG. 1, and is disposed in a way such asto make contact with an interface on the side of the pinned layer 220opposite to the insulation layer 21 side interface.

Next, a description will be given of an operating principle of themagnetoresistance element 1-2 according to the second embodiment.

As a write action from a high resistance condition to a low resistancecondition is exactly the same as with heretofore known technology, inthe same way as in the first embodiment, a description thereof will beomitted. Hereafter, a description will be given, referring to FIG. 4, ofa write action from a low resistance condition to a high resistancecondition. In FIG. 4, arrows 102 and 102A indicate magnetizationdirections. In the second embodiment, it is taken that the compensatedtemperature T_(comp) of the storage layer 20 is 200° C. or more, and thecompensated temperature T_(comp) of the pinned layer 220 is around 110°C.

Firstly, when a write current flows, Joule heat is generated owing tothe resistance (up to 4 kΩ) of the heat assist layer 28-2, the heat istransmitted from the heat assist layer 28-2 to the pinned layer 220, andthe pinned layer 220 is heated (FIG. 4(a)). When the temperature of thepinned layer 220 exceeds the compensated temperature T_(comp) owing tothe heating, the net magnetization of the pinned layer 220 is reversed(FIG. 4(b)). By an STT action being carried out in this condition, thestorage layer 20 receives a torque directed in the same direction as thepinned layer 220, and reverses the magnetization direction at this point(FIG. 4(c)). When the supply of the write current stops, the temperatureof the pinned layer 220 decreases, and the reversed magnetizationreturns to the original condition when the temperature becomes lowerthan the compensated temperature T_(comp). Because of this, themagnetization directions of the storage layer 20 and pinned layer 220are opposed directions, and the write action from the low resistancecondition to the high resistance condition is completed (FIG. 4(d)).

Next, a description will be given of a fabrication method of themagnetoresistance element according to the second embodiment.

Firstly, as shown in FIG. 5a , the drain region 24, the source region25, the gate line 16, the contact portion 17, the word line 18, thelower electrode 14, and the insulation body 23A are formed on thesilicon substrate 15 using a normal CMOS process. Next, as shown in FIG.5b , the heat assist layer 28-2 (Ta of 20 nm thickness), the pinnedlayer 220 (Tb₂₄Fe₅₃Co₂₃ of 5 nm thickness, Fe₁₀Co₉₀ of 1 nm thickness),the insulation layer 21 (MgO of 0.7 nm thickness), the storage layer 20(Fe₁₀Co₉₀ of 1 nm thickness, Gd₂₂Co₇₈ of 2 nm thickness), and the upperelectrode 12 (Ta of 2 nm thickness/Ru of 5 nm thickness) are depositedsequentially using a magnetron sputtering method. As a subsequentprocess is the same as in the first embodiment, a description will beomitted.

In the magnetoresistance element 1-2 according to the second embodiment,the compensated temperature T_(comp) of the Tb₂₄Fe₅₃Co₂₃ used in thepinned layer 220 is around 110° C. Consequently, in the same way as inthe first embodiment, owing to the temperature change of the heat assistlayer 28-2 depending on the size of the write current pulse, it ispossible to write both a low resistance condition and a high resistancecondition with a current of the same polarity.

Third Embodiment

A description will be given of a third embodiment of the invention. Thethird embodiment uses a metal-insulator transition material in the heatassist layer 28-2 in a configuration of the magnetoresistance element1-2 based on the second embodiment. The transition temperature of theheat assist layer 28-2 exists in a range of temperatures from roomtemperature to the compensated temperature of the storage layer 20.

A description will be given of a principle whereby a write action usinga unipolar current is stabilized in the magnetoresistance element 1-2configured in such a way. FIG. 7 is a graph showing a change in theresistivity of the metal-insulator transition material used in the heatassist layer 28-2. The heretofore mentioned metal-insulator transitionmaterial indicates a kind of material whose resistivity increasessharply at a temperature equal to or higher than room temperature, asshown in FIG. 7. For example, (CrV)₂O₃ is applied as this material. Inthe embodiment, a material used is such that a Cr substitution content xof the material (CrV)₂O₃ given above as an example is taken to be in theregion of x=0.06, and a transition temperature T_(T) thereof is taken tobe in the region of 90° C. Also, the compensated temperature T_(comp) ofthe pinned layer 220 is taken to be approximately 110° C., and arelationship is such that T_(T)<T_(comp).

Firstly, when a write current is caused to flow, Joule heat is generatedin the insulation layer 21. When the thickness of the insulation layer21 is 1.0 nm, resistivity (kA) is up to 10 Ωcm, and a resistance value(R) is 1.3 kΩ. Consequently, when taking the write current to be 70 μA,and the write current pulse width to be 10 ns, the element temperaturerises 60° C. owing to the Joule heat, reaching 80° C. In this condition,the temperature of the pinned layer 220 is lower than the compensatedtemperature T_(comp), and a write action from a high resistancecondition to a low resistance condition is realized.

Also, as the element temperature exceeds the transition temperature (90°C.) of the heat assist layer 28-2 when taking the write current to be 75μA and the write current pulse width to be 10 ns, the resistivity of theheat assist layer 28-2 leaps by two digits. As a result of this, theamount of heat generated in the heat assist layer 28-2 increasessharply, and the element temperature rises suddenly to in the region of130° C. Because of this, the element temperature is equal to or higherthan the compensated temperature T_(comp) of the pinned layer 220, and awrite action from a low resistance condition to a high resistancecondition is realized. As a large temperature change is induced withonly a small increase in the current in this way, even when there isvariation in the compensated temperatures of individual elements 1-2manufactured, a stable write action is realized without taking too muchof a current margin.

Next, a description will be given of a fabrication method of themagnetoresistance element according to the third embodiment.

Firstly, as shown in FIG. 5a , the drain region 24, the source region25, the gate line 16, the contact portion 17, the word line 18, thelower electrode 14, and the insulation body 23A are formed on thesilicon substrate 15 using a normal CMOS process. Next, as shown in FIG.5b , the substrate is heated to 350° C., and the heat assist layer 28-2(Cr_(0.012)V_(1.988)O₃ of 2 nm thickness) is deposited using a magnetronsputtering method. Subsequently, the pinned layer 220 (Tb₂₄Fe₅₃Co₂₃ of 5nm thickness, Fe₁₀Co₉₀ of 1 nm thickness), the insulation layer 21 (MgOof 0.7 nm thickness), the storage layer 20 (Fe₁₀Co₉₀ of 1 nm thickness,Gd₂₂Co₇₈ of 2 nm thickness), and the upper electrode 12 (Ta of 2 nmthickness/Ru of 5 nm thickness) are deposited sequentially. As asubsequent process is the same as in the first embodiment, a descriptionwill be omitted.

Herein, a metal-insulator transition material having a transitiontemperature in a temperature range of room temperature to in the regionof 350° C., as does, for example, (CrV)₂O₃, LaSrMnO, or the like, isappropriate as a material of the heat assist layer 28-2. This is becausewhen the pinned layer 220 is heated to a temperature higher than 350°C., there is a danger of the rare earth-transition metal alloy includedin the pinned layer 220 crystallizing.

Also, even though no extremely sharp change in resistivity is exhibitedat the transition temperature T_(T), as with these alloys, it ispossible, even when using a PTC (positive temperature coefficient)material (having a positive temperature coefficient of resistance) whoseresistivity increases owing to a temperature rise in a temperature rangeof room temperature to the compensated temperature, to stabilize a writeaction using a unipolar current according to the same principle. Forexample, LaSrCuO₄, BaTiO₃ doped with a third period element (forexample, BaNaTiO₃, or the like), YBa₂Cu₃O₇, Sr₂Cu₃O₅, LaSrCoO₃, NaNbO₃,BiFeO₃, and the like, are known as this kind of material.

When using the heretofore described PTC material, a kind of materialwhose resistivity always increases in the temperature range of roomtemperature to the compensated temperature may be used but, this notbeing indispensable, provided that the resistivity increases in atemperature range of in the region of ±5° C. of the compensatedtemperature, it is sufficient for the heretofore described action.However, it is desirable that the change of resistance value in therange of ±5° C. is 500Ω or more. For example, when the write current isreduced to around 5×10⁵ A/cm², it can be calculated that at a resistanceof 500Ω there is a contribution to temperature rise of approximately alittle under 10° C. This is because, even when the variation of thecomposition of the rare earth-transition metal alloy in the pinned layer220 in individual magnetoresistance elements 1-2 manufactured is kept towithin ±0.2%, the variation of the compensated temperature is estimatedto be in the region of 7 to 8%, and it is considered that in the regionof 10° C. is necessary as a margin.

Of materials (V_(1-x)Cr_(x))₂O₃ used as the heat assist layer 28-2, amaterial (Cr_(0.006)V_(0.994))₂O₃, wherein x=0.006, has ametal-insulator transition temperature of around 90° C., and theresistivity increases by two digits with this temperature as aborderline. When taking the current value of a write action from a highresistance condition to a low resistance condition to be 70 μA, theelement temperature is 80° C., as heretofore described. Also, whentaking the current value of a write action from a low resistancecondition to a high resistance condition to be 75 μA, the elementtemperature is 130° C., and it is possible to secure a margin of 20° C.with respect to the compensated temperature. Imagining that there are noheat assist layer 28-2, a current of 95 μA would be necessary in orderfor the element temperature to become 130° C. FIG. 8 shows an example ofa relationship between the current caused to flow through the heatassist layer 28-2 and the temperature of the magnetoresistance element1-2. In FIG. 8, the dotted line shows current-temperaturecharacteristics when the heat assist layer 28-2 is formed of the normalresistive material used in the first and second embodiments, and thesolid line shows current-temperature characteristics when the heatassist layer 28-2 is formed of the metal-insulator transition material.As shown in FIG. 8, when the metal-insulator transition material is usedin the heat assist layer 28-2, the current value necessary in order tosecure the same temperature margin drops from I₁ to I₁′. In this way,according to the memory in the embodiment, it is possible to realize astable write action, even when the current is low.

Even when applying the material of the heat assist layer in theembodiment to the heat assist layer 28-1 of the first embodiment, it ispossible to achieve the same benefit as in the embodiment.

Fourth Embodiment

FIG. 9 shows a memory cell 8 using the magnetoresistance elements 1 (1-1and 1-2) shown in FIG. 1 and FIG. 6, and FIG. 10 shows a non-volatilesemiconductor storage device 10 including a cross-point type memory cellarray formed by arraying memory cells 8.

As already described, switching with a unipolar electrical pulse ispossible with the magnetoresistance elements 1-1 and 1-2 of theinvention. The memory cell 8 has a configuration wherein a rectifierelement 9 (for example, a diode) acting as a selector switch isconnected in series to the magnetoresistance element 1. Consequently, bydisposing individual memory cells 8 in an array form, the cross-pointtype non-volatile semiconductor storage device 10 shown in FIG. 10 isformed.

With regard to the manufacture of the individual memory cells 8, forexample, it is possible to form the rectifier element 9 in advance onthe silicon substrate 15 (FIG. 1), and to form the magnetoresistanceelement 1 in a portion above the rectifier element 9. Then, by applyingan electrical pulse with a positive polarity from the storage layer 20or 200 (refer to FIG. 1 and FIG. 6) side of the magnetoresistanceelement 1 in the memory cell 8, it is possible to cause the memory cell8 to carry out an efficient switching.

Meanwhile, a processing temperature necessary for fabricating themagnetoresistance element 1 is in the region of, or less than, the 350°C. necessary as an annealing temperature. Consequently, it does nothappen that the performance of an electrical pulse supply transistor(for example, a MOSFET), or the cell selection switch rectifier element9, formed in a portion below the magnetoresistance element 1 is impairedby the effect of the annealing temperature. It is also possible toincrease the total memory capacity by stacking non-volatilesemiconductor storage devices 10 three-dimensionally. In this case, thenumber of wires increases but, as the wire material can sufficientlywithstand the annealing temperature of 350° C., there is no danger ofthe wires deteriorating because of the temperature.

Next, referring to FIG. 10, a more detailed description will be given ofthe non-volatile semiconductor storage device 10 having a configurationacting as a cross-point type memory cell array. When contents ofinformation to be stored are written into the non-volatile semiconductorstorage device 10, lines among word lines WLi (i=1 to n) correspondingto words accessed are selected by a word line decoder 110, and a signalcorresponding to data to be written into the lines of memory cells 8connected to the word lines selected is applied from a bit line decoder120 via bit lines BLi (i=1 to m) to the corresponding memory cells 8.Word lines of words not accessed are affected by an action of therectifier element (diode) 9 in such a way that no current flows to thememory cells 8. That is, only word lines of words accessed are connectedto a ground. Then, a signal such that a set action or reset action isrealized is applied from the bit line decoder 120, in accordance withdata needing to be written, between the bit lines and word linesconnected to the accessed memory cells 8.

Next, a description will be given of a read action. The bit line decoder120 includes current detection units (not shown) provided correspondingto each bit line. When reading, in the same way as when writing,accessed word lines are selected by the word line decoder 110, andcurrent flowing from each bit line into the word lines is detected bythe current detection units. Therefore, the bit line decoder 120 detectsvoltage values in accordance with the resistance of the memory cell 8corresponding to each bit line, and reads the condition of the memorycells 8 based on the voltage values.

Heretofore, a description has been given of embodiments of the inventionbut, the invention not being limited to the embodiments alreadydescribed, various kinds of alteration, change, and combination arepossible based on the technological idea of the invention.

For example, in the first embodiment, the heat assist layer 28-1 isdeposited on the storage layer 200 in FIG. 1, but this is not limiting.That is, provided that the heat assist layer 28-1 can heat the storagelayer 200, it can be formed in any position in a magnetic tunneljunction portion 13. For example, the heat assist layer 28-1 may beinterposed between the lower electrode 14 and pinned layer 22. The samealso applies to the second embodiment.

DESCRIPTION OF REFERENCE NUMERALS AND SIGNS

-   1, 1-1, 1-2 Magnetoresistance element-   8 Memory cell-   9 Diode-   10, 10-1, 10-2 Non-volatile semiconductor storage device-   11 Bit line-   12 Upper electrode-   13 Magnetic tunnel junction (MTJ) portion-   14 Lower electrode-   15 Silicon substrate-   16 Gate line-   17 Contact portion-   18 Word line-   20, 200 Storage layer (second magnetic body)-   21 Insulation layer-   22, 220 Pinned layer (first magnetic body)-   23, 23A, 23B Interlayer insulation film-   24 Drain region-   25 Source region-   28-1, 20-2 Heat assist layer-   51 Resist portion-   52 Contact hole-   102, 102A Magnetization direction-   110 Word line decoder-   120 Bit line decoder

1. A method comprising: forming a pinned layer, an insulation layer, anda storage layer; and forming a heat assist layer above the storage layerusing reactive sputtering.
 2. The method of claim 1, wherein the pinnedlayer, the insulation layer, and the storage layer are formed usingmagnetron sputtering.
 3. The method of claim 1, further comprisingforming an upper electrode above the heat assist layer using magnetronsputtering.
 4. The method of claim 1, wherein the heat assist layercomprises TaN.
 5. The method of claim 1, further comprising forming aprotective layer between the storage layer and the heat assist layer. 6.The method of claim 5, wherein the protective layer comprises at leastone of Ta or Ru.
 7. The method of claim 1, further comprising forming anupper electrode above the heat assist layer using magnetron sputtering,and wherein the pinned layer, the insulation layer, and the storagelayer are formed using magnetron sputtering.
 8. The method of claim 7,further comprising: forming a resist above the upper electrode;subsequently removing material not below the resist; subsequentlyremoving the resist; subsequently forming interlayer insulation abovethe upper electrode; subsequently forming a hole in the interlayerinsulation above the upper electrode; and subsequently forming a contactin the hole, such that the contact abuts the upper electrode.
 9. Themethod of claim 8, wherein said removing material not below the resistcomprises using ion etching.
 10. The method of claim 8, wherein saidforming a hole in the interlayer insulation comprises usingphotolithography.
 11. The method of claim 1, wherein: the pinned layeris formed above a lower electrode; and the lower electrode is formedabove a portion of a CMOS transistor.
 12. The method of claim 11,wherein the portion of the CMOS transistor comprises a drain region. 13.A method comprising: forming a heat assist layer using magnetronsputtering; and above the heat assist layer, forming a pinned layer, aninsulation layer, and a storage layer.
 14. The method of claim 13,wherein the pinned layer, the insulation layer, and the storage layerare formed using magnetron sputtering.
 15. The method of claim 13,further comprising forming an upper electrode above the storage layerusing magnetron sputtering.
 16. The method of claim 13, wherein the heatassist layer comprises TaN.
 17. The method of claim 13, furthercomprising forming an upper electrode above the storage layer usingmagnetron sputtering, and wherein the pinned layer, the insulationlayer, and the storage layer are formed using magnetron sputtering. 18.The method of claim 17, further comprising: forming a resist above theupper electrode; subsequently removing material not below the resist;subsequently removing the resist; subsequently forming interlayerinsulation above the upper electrode; subsequently forming a hole in theinterlayer insulation above the upper electrode; and subsequentlyforming a contact in the hole, such that the contact abuts the upperelectrode.
 19. The method of claim 18, wherein said removing materialnot below the resist comprises using ion etching.
 20. The method ofclaim 18, wherein said forming a hole in the interlayer insulationcomprises using photolithography.